CDP Neighbor question

A friend came to me asking a question regarding the output below, but given my novice level I have been unable to help. Below is the sh cdp neighbor command from a Cisco 3550 Switch that is connected to a Cisco 2821 router. The question is what do the decimal point after Gig 0/1 signify? For instance, Gig 0/1.8? Also, why would someone have a setup of using the same interface three times? Thanks for any assistance.